ABSTRACTAmong the tools most widely used by a corrosion engineer or technician are a reference electrode and a voltmeter. With them, corrosion potential measurements can be made to assist in determining corrosion of a structure or the effectiveness of a cathodic protection system. However, there are sources of error in these measurements. This paper will discuss some of the more common sources of error and how to reduce them as much as practical.

INTRODUCTIONCorrosion potential measurements made using a reference electrode and a voltmeter are one of the most common measurements made in corrosion engineering. They provide valuable information on corrosion of a structure as well as being the primary means for determining the effectiveness of a cathodic protection system. In fact, the various industry standard criteria for determining the adequacy of a cathodic protection system all depend, in one way or another, on potential measurements. In order to make sound judgments on the condition of a cathodic protection system, it is very important that corrosion control practitioners understand possible sources of error inherent in potential measurements avd use their knowledge and experience to reduce these errors.

MEASUREMENT CIRCUIT

A potential measurement circuit is a simple DC circuit as shown in Figure 1. Figure 1 a is a physical layout of the components while Figure 1 b is an equivalent electrical schematic of this circuit. The driving voltage for this circuit is the potential which exists between the reference electrode and the structure. When the circuit is complete, such as when a measurement is being made, a current will flow through the circuit as a result of this potential. The magnitude of the current flow follows Ohm's law, I = E/R, in that it is inversely proportional to the sum of all the resistances in the circuit. For example, if the circuit potential is one volt and the sum of the resistances is 10 megohm, a tenth of a micro-amp will flow through the measurement circuit.

Voltage drops occur across each of the resistive elements in the measurement circuit. These voltage drops are separate and distinct from the more commonly discussed voltage drops, or IR drops, which are due to external current flowing through the electrolyte. Both measurement circuit voltage drops and external voltage drops become incorporated into potential measurements causing errors. Different methods must be employed to minimize errors caused by each type.

In most cases, resistance of the lead wires and the structure is sufficiently small that the voltage drop which occurs along them during measurements is inconsequential. Using the current values in the above example, if a lead wire or the structure has a one ohm resistance, it will cause a one tenth micro-volt voltage drop. This is well below the detection limit of commonly used meters. Most reference electrodes have an internal resistance on the order of one kilo-ohm. Even if this resistance were to be as high as ten kilo-ohms, the voltage drop across the reference in the above example would only be about one milli-volt. Electrolyte resistance is highly variable ranging from quite low for potential measurements in seawater to very high for potential measurements in semi-dry concrete or soils. The proper strategy is to select a meter whose internal resistance (input impedance) is several orders of magnitude higher than any other resistance in the circuit so that voltage drop across the meter will, for practical purposes, represent the entire voltage drop in the circuit.

ABSTRACTThe influence of wind effects on local atmospheric corrosivity was measured and modeled. Six sets of CLIMAT units were placed among devices that provided various degrees of wind sheltering near a deiced highway. Although each set was exposed to the same relative humidity, there was a 34-fold difference between the average mass loss of the most wind-protected and the least wind-protected sets. This is consistent with the concept that atmospheric corrosion rates depend primarily on salt aerosol deposition rates, which in turn depend on local wind velocity and turbulence patterns. Therefore barriers that reduce the wind velocity and turbulence intensity reduce aerosol deposition rates and consequently corrosivity rates. Detailed modeling of the wind flow patterns around two of the CLIMAT sets confirmed that the corrosivity differences were due to aerosol deposition effects. Terminology could be modified to better reflect the localized nature of atmospheric corrosivity. It is suggested that macrocorrosivity refer to the characterization of an area that is on the scale of kilometres such as a city or county; that microcorrosivity refer to the characterization of locations that are on the scale of meters such as different sites near a building or vehicle; and that nanocorrosivity refer to characterizing spots that are on the scale of centimetres.

INTRODUCTIONThe deposition rate of aerosol particles that contain chloride is considered an influential factor in the corrosion rate of an object exposed to the atmosphere along with relative humidity and exposure to pollutants such as SO2 ~ . The application of the principles of aerosol transport and surface deposition can provide a theoretical framework for explaining and interpreting atmospheric corrosion patterns. The effect of various wind barriers on atmospheric corrosivity was measured near a deiced highway using CLIMAT coupons 2. The airflow patterns near two of these barriers were simulated and their effect on aerosol deposition was assessed.

Aerosol Deposition ModesThere are two modes of aerosol deposition that are relevant for particles in the size range of marine-type aerosols: (i) inertial impaction and (ii) turbulent diffusion. Inertial impaction is significant for objects that are small enough not to cause gross changes in the surrounding air flow pattern. Essentially, some of the upstream aerosol particles are not able to follow the flow lines around the object due to inertia. Examples include devices used for measuring atmospheric corrosivity such as CLIMAT coupons and salt candles 1.

The capture efficiency, 1"1, depends on the upstream fluid velocity at an infinite distance, the target size, the aerosol size and density and the fluid density and viscosity. The nature of capture efficiency for a cylinder determines that the deposition rate is zero until the upstream velocity reaches a certain minimum and then the deposition rate increases roughly linearly with upstream velocity. For practical evaluations, the air velocity two diameters upstream from the surface of a cylinder, termed the approach velocity, may be considered to be an approximation of that at an infinite distance 3.

Aerosol particles are transported via winds from sources, such as salt-water bodies and deiced highways, by convection and turbulent diffusion. Turbulent diffusion can also deposit particles onto surfaces that are normal to the main airflow, although it is less effective than inertial deposition. Many surfaces act as a sink where the concentration of aerosol particles in air is effectively zero. The deposition rate is highly dependent on the wind speed and the shape and size of the object as well as aerosol concentration in

In situ identification of the films formed on alloys of Fe-13Cr-10Ni, Fe-5Cr-10Ni and 304 stainless steel immersed in high temperature, high purity water was performed using Raman spectroscopy and surface enhanced Raman spectroscopy. The films were examined as a function of the dissolved oxygen of the water. The results were complemented by scanning electron microscopy of the oxide films. The films were determined to be a function of the alloy's chromium concentration and the water's dissolved oxygen concentration. The results are consistent with the hypothesis that susceptibility to IGSCC is determined, at least in part, by the identity of the surface film that forms over the grain boundary regions. In the context of the hypothesis, the results can be used to explain (1) the existence of a threshold potential below which IGSCC will not occur, (2) the influence of chromium concentration of grain boundaries on IGSCC and (3) the influence of electrical conductivity of the water on susceptibility to IGSCC.

INTRODUCTIONIn a separate paper we reported the influence of dissolved oxygen concentration of water at 288°C on the films formed on iron [1]. By a combination of in situ Raman spectroscopy (RS) and surface enhanced Raman spectroscopy (SERS) and ex situ scanning electron microscopy (SEM) a number of new facts were discovered.

Several earlier studies had revealed that the film formed on iron in 288°C deoxygenated water consisted of an inner, conformal layer of Fe304 that grows into the iron and an outer layer of loosely packed grains of Fe304 that precipitate from the aqueous phase [2-9]. Our study confirmed these results in the following manner. We had deposited on the original iron surface a layer of gold particles, which act to enhance the Raman spectra of species present on the iron surface, such as its passive film. The gold particles also served as surface markers. The inner layer of Fe304 formed beneath the gold particles showing that it developed by growing into the iron. The outer layer of Fe304 formed on top of the gold particles, indicating that the outer layer resulted from precipitation of Fe304 from the aqueous phase.

In addition, our results reported a number of new observations. First, it was noted that the outer layer of Fe304 grew non-uniformly. Some grains grew and some did not. In addition, for samples with gold particles on their surface, the growth of the outer layer of particles of F%O 4 was preferentially high for particles of Fe304 located close to gold particles. This suggests that the electrochemical reduction reaction is the rate determining step in the growth of the outer layer.

Second, as the dissolved oxygen concentration was increased from 0 to 22 ppb, the corrosion potential was raised by over 160 mV, an increase that was far to large to be accounted for by factors associated with the electrochemical reduction reaction. Since the oxidation rate appeared to decrease over the same range of oxygen concentration even though the identity of the surface film according to SERS remained unchanged, it was proposed that the inner layer of Fe304 increased in protectiveness. For example, a decrease in porosity of the inner layer and/or an increase in its thickness may be responsible for its greater protectiveness.

Third, the rising corrosion potential eventually reached a value (= -400 mV vs. SHE) at which the outer surface region of the outer layer of Fe304 transformed to ct- Fe203. This appeared to complete the passivation process.

The present investigation uses the same experimental techniques of in situ SERS and RS and ex situ SEM as was used in the study of the films formed on iron. The primary purpose is to inv

ABSTRACTStress corrosion cracking and corrosion fatigue commonly initiate at corrosion pits, which serve as stress raisers. Thus, the challenge in predicting the initiation of these forms of stress induced damage to a metal surface in a corrosive medium reduces to the prediction of the initiation and growth of stable pits. Because the stress intensity factor (KI) increases with increasing pit depth (for a constant stress), the transition of a pit into a crack is envisioned to occur when the stress intensity exceeds the critical value for the initiation of a crack (Kiscc). In this paper, we outline a deterministic theory for the initiation of stress corrosion cracking and corrosion fatigue based on the Point Defect Model (PDM) for passivity breakdown and the Coupled Environment Pitting Model (CEPM) for pit growth within the framework of Damage Function Analysis (DFA). Once a crack initiates, the Coupled Environment Fracture Model (CEFM) and the Coupled Environment Corrosion Fatigue Model (CECFM) for stress corrosion cracking and corrosion fatigue, respectively, describe continued, stress-augmented propagation. The principals of DFA are illustrated by reference to the development of localized corrosion damage on aluminum exposed to sodium chloride solution, with emphasis on illustrating the interplay between stress-related and electrochemical effects. Practical applications in describing the failure of condensing heat exchangers and low-pressure steam turbines are also discussed.

INTRODUCTIONThe development of effective localized corrosion damage prediction technologies is essential for the successful avoidance of unscheduled downtime in complex industrial and infrastructural systems and for the successful implementation of life extension strategies. Currently, corrosion damage is extrapolated to future times by using various empirical models coupled with damage tolerance analysis (DTA). In this strategy, known damage is surveyed during each subsequent outage, and the damage is extrapolated to the next inspection period allowing for a suitable safety margin. Extrapolation is generally carried out using fracture mechanics models that rarely contain environmental information in explicit form. For example, the NRC approved expression for estimating the rate of crack propagation in low-pressure steam turbine discs contains only two independent variables; namely, the yield strength and the stress. While environmental information may have been incorporated inadvertently through calibration, the lack of environmentally related independent variables severely restricts the usefulness of the model for predictive purposes, especially for identifying optimum operating chemistry conditions.

As the authors has argued elsewhere [1-3], for the reasons given above, DTA is inaccurate and inefficient, and that in many instances it is too conservative. Instead, it was proposed that damage function analysis (DFA) is a more effective method for predicting the progression of damage, particularly when combined with periodic inspection. DFA is based on the use of the damage function (DF) to describe the evolution of damage, which accumulates in a progressive manner (new damage nucleates while existing damage grows and dies). An effective DFA algorithm must therefore include methods for calculating the pit nucleation rate, the pit growth rate, and the pit delayed repassivation rate, preferably in a deterministic manner. Although corrosion is generally complicated mechanistically, a high level of determinism has been achieved in various models of both general corrosion and localized corrosion that can be used to predict accumulated damage in the absence of large calibrating databases.

ABSTRACTStress corrosion crack growth studies have been performed in high temperature, ultra high purity water on unsensitized stainless steels and alloy 600 as a function of martensite, yield strength, corrosion potential, temperature, and hydrogen fugacity. Parallel experiments were performed to evaluate the hydrogen permeation rate. SCC response paralleled the yield strength, corrosion potential, and temperature, and was substantially independent of the martensite content per se, the hydrogen fugacity, and the hydrogen permeation rate. The implications to fundamental crack advance processes in iron and nickel alloys are discussed.

INTRODUCTIONDespite the relative narrowness in alloy compositions and similarity in the environments used in light water reactor systems and many common SCC characteristics [ 1-7], there remains a tendency to fragment stress corrosion cracking (SCC) into small, unique modes with individualized mechanisms and dependencies. Many common grades of structural materials are used in boiling water reactor (BWR) and pressurized water reactor (PWR) - even across many companies and designs -with heavy reliance on similar stainless steels, pressure vessel steels, and nickel alloys and weld metals. The environmental conditions are also quite similar among BWR and PWR primary systems [1,2,4-7], with it now being acknowledged [8] that the crack tip is deaerated and at low potential in all cases.

The advent of NobleChem TM, which should be implemented in essentially all U.S. and many foreign BWRs by 2002, creates low potential conditions on most surfaces in BWRs. This produces conditions even more closely aligned to PWR primary systems, which differ only in: coolant additives that shift the pH at temperature from 5.6 to 7.0; H2 fugacity (=100 vs 3000 ppb H2); and temperature (the PWR primary is up to 35 °C hotter, 50 °C in the PWR pressurizer). Of these, temperature has the most universal effect on SCC.

The subdivision of and unique interpretations applied to SCC in closely related systems extends to the underlying mechanism of crack advance. By any view, SCC is a complex phenomenological process with 10 to 20 important engineering parameters whose strong inter-dependencies cause the effect of any given parameter to s h i f t from strong to subtle as the other parameters change. It is this " s h i f t i n e s s " - combined with a wide distribution in the adequacy of SCC measurements - that is largely responsible for the fragmentation of SCC into small, little sub-modes.

Underlying the complex phenomenology and the fragmented view of SCC is residual ambiguity in the causal, mechanistic underpinnings of SCC. Hypotheses of stress corrosion crack advance range from brittle film cleavage [9,10], to internal oxidation [ 11], to adsorption - decohesion [ 12], to enhanced surface mobility [ 13], to creep rupture, to film rupture / slip oxidation [ 1-7,14], to hydrogen assisted cracking [12,15-17], and beyond. Of these, the latter two are widely regarded as the most promising general descriptions of SCC in hot water environments, and it is the objective of this paper to evaluate several factors (martensite, yield strength, hydrogen fugacity, temperature) and phenomena (crack growth rate, hydrogen permeation) that should strongly influence the rate of hydrogen assisted crack advance mechanisms.

EXPERIMENTAL PROCEDURES

Crack growth specimens were machined as compact type specimens (0.5T for cold worked materials, and 1T for the annealed materials) with 5% side grooves on each side. Linear elastic fracture mechanics criteria were fully satisfied for the stress intensity - specimen size - yield strength conditions employed. The composition of the

ABSTRACTOne of the major problems encountered in operating pressurized water reactor (PWR) steam generators is the accumulation of metal oxide deposits on the secondary side. A new method of controlling iron deposition in a PWR steam generator has been developed. This method consists of continuously feeding a high purity polymeric dispersant to keep the corrosion products entering the steam generator in suspension until they can be filtered from the blowdown. The paper describes the criteria for designing a polymer along with the steps necessary to qualify the selected material for evaluation in an operating PWR. This includes a detailed discussion of polymer characteristics, performance requirements, materials compatibility and potential implications for plant operation.

INTRODUCTIONMetal oxides and other contaminants enter PWR steam generators during operation, but usually only a small amount of the total metal oxides entering systems are removed through the blowdown. The remaining oxides continue to build up and deposit in the steam generators. The majority of the deposit found in steam generators is composed of iron oxide (Fe304) along with other metal oxides, depending upon the materials used in the construction of the balance of the system. 2,3

Deposits form on heat transfer tubes, tube sheets and tube support plates. These deposits have been associated with under-deposit-corrosion, and this can make it necessary to sleeve or plug tubes. 4'5'6'7'8 Excessive deposition on the heat transfer surfaces causes a loss in thermal efficiency, which can result in both pressure and power loss. Secondary side corrosion has been implicated as the cause of costly unscheduled outages and steam generator replacement. A common cause of tube repairs is stress corrosion cracking (SCC). 9

Several initiatives have been undertaken by the nuclear power industry to reduce problems associated with deposit accumulation in steam generators. These initiatives fall into three major categories; reducing the iron entering steam generators from the condensate returned from the balance of the plant, inhibiting localized corrosion in steam generators through the use of chemistry control and chemical additives, and off-line mechanical or chemical cleaning.

One approach taken to reduce the iron entering generators has been to use amines and ammonia as pH control additives on the secondary side of PWRs. These additives can be used either alone or in combination. When compared to ammonia, the amines provide the benefits of higher steam generator pH and better pH control throughout the condensate system. As a result, corrosion is reduced, which in turn lowers the transport of iron corrosion products back to steam generators. Amines such as ethanolamine, morpholine, dimethylamine and methoxypropylamine have been used successfully in operating PWRs.

Although great strides have been made at reducing the amount of iron entering steam generators, deposits still exist. Over time, even trace levels of feedwater iron can accumulate to unacceptable levels in the steam generator because of poor iron transport. Where deposits are present, molar ratio control and boric acid have been used in an attempt to minimize corrosion by controlling the crevice solution pH. 1°

Many utilities have undertaken programs to remove deposit from their steam generators. Techniques used include sludge lancing, bundle flushes, pressure pulse cleaning, crevice flushes, chemical soaking and chemical cleaning. These processes take place off-line and are typically scheduled during refueling outages. All of these methods are time consuming, expensive and most only remove a portion of the accumulated deposit.

ABSTRACTOil and gas transmission pipelines are subject to internal and external agents that can cause corrosion affecting their safety, integrity, and profitability. Restoring pipelines to a safe operating condition is the main goal of inline inspection (ILI) using state-of-the-art Smart Pigs. These tools travel through the full length of pipelines gathering detailed information that is used for the assessment of both the internal and the external surfaces of the line. Ultrasound ILI tools perform direct measurements of the remaining wall thickness of the pipe. The analysis of an ultrasound ILI run determines the residual strength of the pipeline at the time of the inspection. Furthermore, the comparison of recurrent ultrasound runs establishes patterns of defect growth. Under this light the interpretation of the data leads to an assessment of the dynamics of the corrosion phenomena occurring in pipelines.

This paper presents the results of applying remaining strength criteria for the evaluation of corrosion defects detected by an ultrasound tool in transmission lines. The impact of defect growth on the integrity of transmission pipelines is illustrated by comparisons of sets of data collected from recurrent ultrasound inline inspections of a pipeline system.

INTRODUCTIONThe concept of in-line inspection (ILI) of pipelines dates back to the sixties when the first "smart pigs" were introduced commercially. In-line inspection refers to the inspection of an operating pipeline by means of a free-swimming tool displaced by the fluid within the line. The original inspection tool (or "smart pig") used the magnetic flux leakage (MFL) principle to detect metal loss anomalies but had limitations sizing the features to the detail required for integrity analysis.

A second generation of MLF pigs evolved through the eighties and nineties with powerful magnets, large number of small sensors, digital on-board data processing, and other innovations derived from progress in microelectronics. A substantial development in MFL data processing came with the increased availability of computer power. Large amounts of digital data could be evaluated applying complex algorithms with the use of sophisticated computer systems.

The enhanced data characterization and dimensioning of metal loss features allowed high resolution analysis of the records collected by second generation MFL pigs. Higher resolution made it feasible to apply remaining strength engineering calculations with an acceptable degree of confidence.

A similar development took place in the eighties, when Pipetronix (now ~art of The PII Group) adapted the ultrasound NDT for the ILI of pipelines. The UltraScan TM WM ( ) pig uses compression ultrasound waves (5 MHz sound frequency) to scan and measure the remaining thickness of the pipe wall. The ultrasound technique (UT) differs from MFL in that the measurement does not require mathematical post processing. The UT readings are true direct measurements of the actual wall thickness in any given point of the pipeline. The proprietary design of the UT pig sensor carrier, illustrated by Figure 1, allows the detailed assessment of corrosion affecting the steel surface (internal and external) and the presence of mid-wall defects (inclusions, laminations) over tile full length of the pipeline. The defect dimensions established by the ultrasound analysis can be used to establish the remaining strength of the corroded spot applying standardized calculations such as ASME B31G I. Furthermore, the digital remaining wall thickness ultrasound values of corroded areas can be imported to more sophisticated (and more accurate) analysis procedures that use river-bottom profiles such as

ABSTRACTThe corrosion behavior and mechanisms of various materials within supercritical water oxidation (SCWO) systems are reviewed. The materials degradation by different aggressive ions is also summarized. The monitoring and detecting technologies are synopsized. The research progress and intending emerging research topics about SCWO in China are proposed.

INTRODUCTIONWith the development of the modem industry, there is in excess of 400 billion tons of sullage, 3 billion tons of solid contamination that are drained into the environment every year. So it is an urgent need to search for an efficient and safe waste handling method. Supercritical water oxidation (SCWO) is an emerging technology to process many organic wastes and has been shown to have several benefits to handling dilute wastes in the range 1 wt%-20 wt% which are not suitable for disposal by either incineration or landfill. Typical destruction and removal efficiencies can exceed 99.99% for normal operating conditions of 25 MPa, 600°C, and residence times of 60s or less. At normal operating conditions, hydrocarbons are converted to CO2 and water. Heteroatoms such as phosphorus and sulfur are converted to phosphate and sulfate anions, which, depending on pH control, will remain as their respective acids, or if neutralized may precipitate out as salts. Nitrogen heteroatoms are abstracted to form primarily N2 ~-3.

As a result of the relatively low operating temperature, NOx and SO2 compounds are not produced which is formed under higher temperature conditions. The latter may be particularly important during the destruction of explosives that produce nitrogen oxides during incineration 4' 5.

Pure water has a critical point at 374°C and 21.8 MPa. As the critical point is approached, the density of water changes rapidly as a function of temperature and pressure. The properties of supercritical water are significantly different from liquid water at ambient conditions. The density of supercritical water is intermediate between that of liquid water (1000 kg*m 3) and low pressure water vapor (<1 kg*m3). Typically, at SCWO conditions, water density is approximately 100 kg*m 3. The dielectric constant of water at 25 MPa drops from approximately 80 at room temperature to 2 at 450°C, and the ionic dissociation constant decreases from 10 ~4 at room temperature to 10 .23 at supercritical conditions. These changes result in supercritical water acting essentially as a non-polar dense gas with solvation properties approaching those of a low-polarity organic. In the critical region, organic materials and noncondensible gases become soluble 6. For example, benzene (C6H6) at temperatures above 300°C and 25 MPa is completely miscible in water over all concentrations. Gases such as oxygen (02), nitrogen, carbon dioxide and even methane are also completely soluble in supercritical water 7. Conversely, the solubility of inorganic salts in supercritical water is extraordinarily low. For instance, at 25 MPa and 25°C, calcium chloride has a maximum solubility of 70 wt%, which decreases to -3 ppm at 500°C and 25 MPa. With these solvation characteristics, supercritical water is an ideal medium for the oxidation of organics contained in aqueous waste streams.

In SCWO waste treatment process system, aqueous organics and oxygen come together at moderate temperatures (>_400°C) and high pressures. Spontaneous oxidation of the organics liberates heat and raises the temperature to levels as high as 650°C. Organic destruction occurs quickly, reactor residence times being typically less than 1 rain. The combustion products include water, carbon dioxide and molecular nitrogen. Low solubility inorganic salts precipitate and may be removed as brin

ABSTRACTFollowing short-term and long term electrochemical evaluations of twenty-three cast alloys varied around the baseline alloy composition of 3.5 weight percent (w/o) zinc, 1200 parts per million by weight (ppmw) silicon and 150 ppmw indium, scanning electron microscopic evaluations were made including elemental evaluations of interesting features. The presence, location and electrochemical behavior of Fe/Si rod impurities within the bulk alloy was documented. Some surface segregation of excessive element additions appearing to have resulted in passivation was also documented.

INTRODUCTION AND BACKGROUNDThis effort, involving the study of alloying effects within the sacrificial aluminum alloy anode composition now commercially available as Galvalum III°) (GV3), took place during 1987-1988 when A.G.S. (Terry) Morton served as Visiting Scientist at the Materials Research Laboratory, (now the Aeronautical and Maritime Research Laboratory), Defence Science and Technology Organization (DSTO), Melbourne, Australiak At the time of the study, the GV3 composition had been patented:and is presented as part of Table 1. While the values in the three patent claims tend to become more narrow as one proceeds into the claims, at that time there was nothing published regarding the effect of the various constituents and/or impurities. This has in part been rectified 3'4'5 with published data taken from

test samples of a large variety of commercial runs. For the effort now being presented, approximately 24 compositional variations were prepared and characterized with respect to electrochemical behavior

(1) Tradename

and macrostructural/microstructural evaluations of the tested pieces. In addition to evaluating the major additive elements (zinc (Zn), silicon (Si), and indium (In)), and the normal impurities (iron (Fe) and copper (Cu)), the potential benefits of adding titanium (Ti) or manganese (Mn) as grain size refiners was investigated. The possibility that Ti or Mn might allow higher levels of Fe and/or Cu impurities without losses of coulombic efficiency was also considered. The U.S. Navy had, in the meantime, tested GV3 material prepared initially with a drafted military specification (MIL-SPEC) followed by testing a published composition in MIL-A-24779. Those compositions are included within Table 1.

The detailed results from this program have been published ~. The data from that document have been reevaluated and are being presented in two parts. The first part (CORROSION/01 P/N 01506) covered the experimental procedures and the electrochemical test results. This portion (Part 2) will present the results from the physical metallurgy examinations of the as-prepared and as-tested samples.

EXPERIMENTAL

Anode Preparation

A series of anode compositions (Table 2) was prepared from elemental or master alloy stock. Each of the anode compositions was cast into split steel molds after blending the constituents and melting them in an electric induction furnace. The 99.99 percent pure aluminum melt stock, coded AP, had trace analyses as shown in the table. Of interest were the low levels of iron and copper, and lack of dominance of any single trace element.

The mold surfaces and crucible were coated with a thin layer of alumina to prevent surface contamination and two trial melts were cast sequentially using "scrap" stock, coded AM. This process of melting, casting (then taking a sample for analysis), re-melting, casting and re-analyzing was used to check for elemental pick-up or volatilization during melting of the metal charge. As can be seen in the table, no increase in Fe or Cu contamination was observed.

ABSTRACTThe new NiCr20Fe14Mol 1WN filler metal is characterized by exceptional resistance to pitting and crevice corrosion, no sensitiveness to chloride induced stress corrosion cracking and shows excellent me- chanical properties, e.g. 0.2 %-yield strength. Because the alloy is practically free of stable nitride formes like niobium and titanium, no nitride formation during welding of super austenitic, duplex and super du- plex steels is possible, which proves the alloy to be superior to alloy 625.

INTRODUCTIONSuper austenitic, duplex and super duplex stainless steels gain increasing market shares because of their exceptional combination of corrosion resistance in salt water and various mineral acids and attrac- tive mechanical properties at ambient temperatures, e.g. 0.2 %-yield strength which is commonly used as a design value.

Matching filler metals for above mentioned alloys are available but suffer decreased corrosion resis- tance because of micro and macro segregations in the cast microstructure of the weld metal.

Therefore it is necessary to apply overalloyed filler metal to achieve at least the same corrosion re- sistance. NiCrMo-filler metals provide satisfactory corrosion resistance, but cannot beware the high me- chanical properties of the parent metal in the as welded condition at ambient temperature.

To take care of this need alloy 50 has been developed. This ahoy is characterized by:

? a high general and local (pitting and crevice) corrosion resistance in various organic and mineral acids, caustic solutions and fused salts,? high mechanical strength at ambient temperature up to 550 °C,? good weldability and fabricability,? reasonable price / property ratio.

Because of almost universal applications for super austenitic, duplex and super duplex steels, alloy 50 might reduce hand stocking of various different filler metals, which generates high costs, logistical [1, 21 problems and accelerated damper of mix up

According to equation 1 the PRE (Pitting Resistance Equivalent) is in the range of 55 - 60 which predicts a critical pitting and crevice corrosion temperature in 10 % FeCl3-solution of 85 °C and 65 °C, respectively [3]

PRE = % Cr + 3.3 (% Mo + 0.5 % W) + 30 % N (1)

A nickel content of more than 50 wt.-% guarantees a high resistance to stress corrosion cracking [4, 51 and caustic salts [6]

For ambient temperature, 450 °C and 550 °C 0.2 %-, 1.0 %-yield strength and tensile strength, as well as the reduction of area are given Table 2 for alloy 50 Ill

WELDING

As a criterion of weldability, testing of the hot cracking behavior in the Modified Varestraint Test (MVT) of the Bundesanstalt ftir Materialforschung und -prtifung (BAM) has proven to be of increasing importance for materials considered as filler metals. In such a test a specimen (100 x 40 x 10 mm 3) is melted with a GTAW torch under defined conditions over a specific length and mechanically bent during this procedure tT, sl. The total length of the cracks visible on the surface at a magnification of 25x is then determined as a function of the applied bending strain and serves as a measure of the sensitivity to hot cracking. The results for different heat inputs are shown in Figure 1. It can be seen that in this test the new alloy 50 exhibits for 7.5 kJ/cm heat input the lowest sensitivity t